• Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!

Rail Signals

Status
Not open for further replies.

FastTrax

Member
Joined
8 Jul 2020
Messages
84
Ok i tried to google this but not much luck and i know the train operators know better than us etc etc.

but i am curious, why the train signals are so small, or shall i say not large. its a very critical role driving a train and lot of lives depend on it stopping at the signal but if i was designing a light i will make so big enough it cant be missed and also other mechanism like spray water on the window of the train like 4 miles before the red signal (ok this might be over the top but you get what i mean).
also i am sure this must be already happening and some train already might have this but getting the driver informed on the cab so he doesn't need to look outside for the signal... i am sure in summer the glare and sun shinning behind the signal makes it hard for the driver to read it.
but my question is who decide the size and shape etc etc. and why so small. i would like to hear from people in the know
many thanks
 
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R

RailUK Forums

ComUtoR

Established Member
Joined
13 Dec 2013
Messages
9,398
Location
UK
They aren't small by any means and are quite easy to read.

Water on the window - Trains have wash/wipers
Summer glare is tricky but the new LED style is a lot more visible and the 'hot spots' are a lot better than the previous design.
Size/Shape etc can be googled. The requirements are found on the RSSB website. (Size/Shape etc) (Sighting requirements)
 
Last edited:

LCC106

Established Member
Joined
16 Nov 2011
Messages
1,301
Oh dear! Not sure how to respond to this one! Signals are not small. There are searchlight types and LED types in Track Circuit Block area, which are easy to see. The Automatic Warning System alerts drivers to yellow and red signals using a horn sound. On encountering these you put your brake in to slow down and stop if required. The sun can be an issue at different times of the day and year but your route knowledge alerts you to these factors so you can take appropriate action and remain alert to such signals. As for in cab signalling, have a search on here.
 

swt_passenger

Veteran Member
Joined
7 Apr 2010
Messages
31,263
I expect all rail signals are aimed accurately to centre the light source at the optimum point on the approach. They can presumably be far more focussed than a similar sized road traffic signal, because the approaching driver’s position is guaranteed. As well as the point about AWS, in the minority of cases where sighting time is reduced compared to ideal, there’ll be a banner repeater on the approach to the signal.
 

Ken H

On Moderation
Joined
11 Nov 2018
Messages
6,271
Location
N Yorks
A light on a stick can be quite small. but railway signals and some road traffic light have a surround to reduce glare. This must make them easier to see when driving into the sun.
maybe a driver can comment.
 

Lucan

Established Member
Joined
21 Feb 2018
Messages
1,211
Location
Wales
Water on the window - Trains have wash/wipers
Oh dear! The OP meant (I think) deliberately spraying water on the cab window to alert the driver to a red signal ahead. He is unaware of audible warnings in cabs.

Are the lenses of railway signals any smaller than road ones anyway? I've never measured them but I have the impression they are larger, and brighter too. There is also the fact that train drivers know from route training where signals are sited, unlike the road where drivers can be stangers to the area.

I have worked in trackside testing. Someone in another team had some equipment working off a portable generator by the trackside at night. The equipment had a tiny red "ON" indicating light, an LED about 8mm diameter. After a few trains had passed without incident, a fast approaching train went into full emergency braking and came to a halt a few hundred yards past the point. The driver walked back to them, furious for their having displayed the red light. There were some uncomfortable explanations to be made, both on the spot and in the manger's office next day.
 

ComUtoR

Established Member
Joined
13 Dec 2013
Messages
9,398
Location
UK
Oh dear! The OP meant (I think) deliberately spraying water on the cab window to alert the driver to a red signal ahead.

I thought he meant to ensure the window was clean and clear for sighting :/
 

pdeaves

Established Member
Joined
14 Sep 2014
Messages
5,632
Location
Gateway to the South West
The actual light in a signal (as opposed to the full housing) can appear small to an onlooker if viewed from the 'wrong' position. As someone else said further up, the light beam is controlled to point to an exact place where the driver will view it. What the driver sees is not small at all.
 

FastTrax

Member
Joined
8 Jul 2020
Messages
84
wow so much good information. thanks for replying so quickly. i was just reading about unfortunate incidents where drivers miss the signal and was wondering if the shape size and other thigns i mentioned above can help. but it seems they are already quite adequate.... spray on the window... lol that was way to the extreme i know... i meant the driver get sprayed on the window to alert him, but its sound crazy and wont be possible. well thanks again, you guys have answered it quite informatively. have a nice day
 

Llanigraham

Established Member
Joined
23 Mar 2013
Messages
6,073
Location
Powys
Please, don't tell the OP about semaphore signals and the lights behind the spectacle plates of those!
 

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
24,793
Location
Nottingham
The actual light in a signal (as opposed to the full housing) can appear small to an onlooker if viewed from the 'wrong' position. As someone else said further up, the light beam is controlled to point to an exact place where the driver will view it. What the driver sees is not small at all.
This also helps reduce the risk of drivers on nearby tracks reading the wrong signal. Road vehicles can approach from a variety of angles so road traffic signals give out a much wider light beam. Another difference is road traffic signals have to be readable by colour-blind people so the red is always at the top and for those people the position of the light is important, so must be discernable a good distance away. Train drivers aren't allowed to be colour-blind and may observe the signal from far enough away that they can't tell if the light is at the top or the bottom - indeed many modern signals display different colours through the same lens. Most railway signals are vertically mounted with the red at the bottom, but occasionally one has to be sideways or "upside down".
 

John Webb

Established Member
Joined
5 Jun 2010
Messages
3,047
Location
St Albans
Signal makers for many years have supplied colour-light signals with different beam angles depending on the distance at which they need to be seen and the speed of approach. The resignalling of a line is designed by professional signal engineers, usually working with a 'signal sighting committee' to sort out any potential problems.

As others have mentioned above, modern signalling has the back-up of several forms of audible warning in the cab and links to the braking systems of trains to minimise the chance of a signal being passed at danger.
 

scotraildriver

Established Member
Joined
15 Jun 2009
Messages
1,626
Semaphore signals are small and very poor at night. I work in an area where we go from a semaphore to LED, the difference is astronomical. Searching around in fog trying to find the candle that is a semaphore is quite unacceptable to me on the modern railway. The sooner these relics are consigned to history the better.
 

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
24,793
Location
Nottingham
Semaphore signals are small and very poor at night. I work in an area where we go from a semaphore to LED, the difference is astronomical. Searching around in fog trying to find the candle that is a semaphore is quite unacceptable to me on the modern railway. The sooner these relics are consigned to history the better.
Most (all?) have now been fitted with electric lamps. They were even worse with until quite recently with the old oil lamps.
 

BigB

Member
Joined
20 Dec 2018
Messages
266
Location
Scotland
There are many good videos on YouTube from the cabs of units that demonstrate just how visible the signals are (and allow a good comparison with e.g. Semaphore).
It is reassuring that they are so visible, and unlike with road users the drivers know where they are, and if one is not showing then they know which one is at fault and to call it in immediately.

LED multi-aspect lights are very bright at night, and there must be a real art to positioning lights so that not only are they optimally placed for approaching trains but that they are also have no conflicting background, especially in areas where the next section is also visible.
 

bramling

Veteran Member
Joined
5 Mar 2012
Messages
17,685
Location
Hertfordshire / Teesdale
There are many good videos on YouTube from the cabs of units that demonstrate just how visible the signals are (and allow a good comparison with e.g. Semaphore).
It is reassuring that they are so visible, and unlike with road users the drivers know where they are, and if one is not showing then they know which one is at fault and to call it in immediately.

LED multi-aspect lights are very bright at night, and there must be a real art to positioning lights so that not only are they optimally placed for approaching trains but that they are also have no conflicting background, especially in areas where the next section is also visible.

One point of note, for those who watch cab ride type videos, the signal aspects show up way more in real life than they do on a tv or computer screen. Filament lamps in particular where they still exist exhibit a characteristic “sparkle”, modern LEDs lack this but people seem to like them because they do tend to be a bit brighter.

LEDs in housings designed for filament lamps can be found in some areas (ECML out of King’s Cross is one such example - here the filament lamps have all been replaced but keeping the old signal heads). Some people feel this is an optimum arrangement, as some of the purpose-build LED signal heads aren’t that well regarded.
 

Irascible

Established Member
Joined
21 Apr 2020
Messages
1,988
Location
Dyfneint
wow so much good information. thanks for replying so quickly. i was just reading about unfortunate incidents where drivers miss the signal and was wondering if the shape size and other thigns i mentioned above can help. but it seems they are already quite adequate.... spray on the window... lol that was way to the extreme i know... i meant the driver get sprayed on the window to alert him, but its sound crazy and wont be possible. well thanks again, you guys have answered it quite informatively. have a nice day

Audible in-cab warnings have been around for many many decades - GWR ATC which is similar operationally to AWS ( for distant signals ) dates from 1905 iirc - but they aren't infalliable as was proven even in the 1990s ( when we really should have had something more capable, but that's a very old debate ). The ultimate answer is to bring the signalling into the cab, as is slowly happening. Worth reading about signalling systems if you're even remotely interested in that sort of thing.

Audible out-of-cab systems are even older, they involved putting detonators out on the rails though...

If I'm remembering details right GWR ATC actually applied the brakes every time & you had to cancel the application, which I guess is fine for old vacuum brakes but not so hot for more modern systems.
 

norbitonflyer

Established Member
Joined
24 Mar 2020
Messages
2,274
Location
SW London
Most railway signals are vertically mounted with the red at the bottom,.

This is, of course, the reverse of the arrangement on the roads. The reason, as I understand it, is that with the lights stacked vertically there is a possibility of one light being obscured by something (snow, a bird.......) on the lens hood of the light below. This won't happen with the light at the bottom of the stack, so the most safety-critical light is put there. I have noticed an exception when there is a 3-aspect signal with no green (that is, double yellow is the least restrictive aspect it can show) where the red was laced between the two yellows to increase their separation. The green is usually put there.

On roads, I assume red is at the top to make it less likely to be hidden behind tall vehicles. Signal sighting committees and the block system make such an eventuality much less likely on the rails.
 

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
24,793
Location
Nottingham
This is, of course, the reverse of the arrangement on the roads. The reason, as I understand it, is that with the lights stacked vertically there is a possibility of one light being obscured by something (snow, a bird.......) on the lens hood of the light below. This won't happen with the light at the bottom of the stack, so the most safety-critical light is put there.
I think that's part of the reason, but it's also to get the most safety-critical lamp closest to the driver's line of sight. For example on the rare occasions a colour light is mounted very low down (often as a "co-actor" to repeat a nearby high signal with poor sighting) the red is at the top. Of course in that case if it was at the bottom it might be obscured by debris on the ground...
 

Lucan

Established Member
Joined
21 Feb 2018
Messages
1,211
Location
Wales
Another difference is road traffic signals have to be readable by colour-blind people so the red is always at the top and for those people the position of the light is important, so must be discernable a good distance away. Train drivers aren't allowed to be colour-blind
As well as postioning, the green of road traffic traffic lights has a blue component which helps red-green colour-blind drivers to distinguish it from the red. Railway signal greens however are a more pure green. The difference is obvious if you ever see them in the same view.

In fact there are other countries (including Japan, USA and Canada) where road traffic lights are sometimes horizontal. This can occur where they are mounted on wires stretched across the road.

for those who watch cab ride type videos, the signal aspects show up way more in real life than they do on a tv or computer screen
That's right. It is disappointing how poorly the signals show up in those videos, in colour as well as brightness. In real life I find modern road signals too bright and make it hard at night to see what lies beyond them - someone crossing the road perhaps. I was never a fan of the "brighter the better" at night approach.
 

scotraildriver

Established Member
Joined
15 Jun 2009
Messages
1,626
thats the whole point of route learning to know the position of signals
I'm fully aware of where the signals are. But not bring able to see them until you are so close causes alot of delay as you unnecessarily crawl towards a signal that's actually off because its so dim.
 

pdeaves

Established Member
Joined
14 Sep 2014
Messages
5,632
Location
Gateway to the South West
thats the whole point of route learning to know the position of signals

I'm fully aware of where the signals are. But not bring able to see them until you are so close causes alot of delay as you unnecessarily crawl towards a signal that's actually off because its so dim.
Quite. It's a performance issue, not (necessarily) a safety issue.
 

Ken H

On Moderation
Joined
11 Nov 2018
Messages
6,271
Location
N Yorks
I was passenger in a car in fog between Settle and long Preston some years ago. The starter from Settle Jct has been a colour light for years, and is clearly visible from the road. The driver (not a confident driver) started to brake at what he thought was a road hazard.

So how does the railway cope with spurious non railway lights that may confuse a driver?
(Hell of a problem with navigation lights at sea. Try finding the buoy (White flashing light) at the entrance to the Hamble river from all the bright lights in the oil installations)
 

swt_passenger

Veteran Member
Joined
7 Apr 2010
Messages
31,263
So how does the railway cope with spurious non railway lights that may confuse a driver?
(Hell of a problem with navigation lights at sea. Try finding the buoy (White flashing light) at the entrance to the Hamble river from all the bright lights in the oil
There’s a good example at Fratton, down direction, there’s a black “sight screen” on the top of the cutting wall that blocks out the road traffic lights at the nearby road junction. It’s about half way between footbridge and road bridge, you can see it’s shadow on the tracks. From the google street view roadside it just looks like a blank advertising hoarding.

I think we had a thread with examples of this type of screen a few years back.
 
Last edited:

pdeaves

Established Member
Joined
14 Sep 2014
Messages
5,632
Location
Gateway to the South West
So how does the railway cope with spurious non railway lights that may confuse a driver?
A 'sighting committee' (made from drivers' representatives and others) will assess whether the signal is OK or whether other mitigations are needed (e.g. move the signal a little, raise/lower it a bit, put screens up, vegetation management, etc.)
 

Ken H

On Moderation
Joined
11 Nov 2018
Messages
6,271
Location
N Yorks
A 'sighting committee' (made from drivers' representatives and others) will assess whether the signal is OK or whether other mitigations are needed (e.g. move the signal a little, raise/lower it a bit, put screens up, vegetation management, etc.)
That makes sense. Then the gas board come along and puts up some temporary traffic lights next to the railway....
 

Islineclear3_1

Established Member
Joined
24 Apr 2014
Messages
5,810
Location
PTSO or platform depending on the weather
The other issue around signal sighting is when the approach is on a tight curve. It's no good if the signal aspect comes into proper view (i.e. maximal brightness) once the driver has brought his train around the curve (especially) at speed and thus the signal has to be angled properly to ensure optimum line of sight from a decent distance

Signals that could be difficult to see (e.g around tight curves/obstructing bridges/station canopies etc) often have "repeaters" sited in advance so that the driver has prior warning of whether he has a "proceed" or "stop" aspect
 

MarkyT

Established Member
Joined
20 May 2012
Messages
6,232
Location
Torbay
Audible in-cab warnings have been around for many many decades - GWR ATC which is similar operationally to AWS ( for distant signals ) dates from 1905 iirc - but they aren't infalliable as was proven even in the 1990s ( when we really should have had something more capable, but that's a very old debate ). The ultimate answer is to bring the signalling into the cab, as is slowly happening. Worth reading about signalling systems if you're even remotely interested in that sort of thing.
The French 'Crocodile' system is even older, first developed in the 1870s using an electrical contact technique. Initially, it just operated a solenoid valve to sound the steam whistle for a cautionary aspect at a distant signal, but was later enhanced to work in the same way as GWR ATC and BR AWS, also requiring an acknowledgement or cancellation to avoid an automatic full brake application. Then there are early 'smash' signals where the semaphore arm is deliberately arranged to be foul of the train's profile when at danger! I guess a mechanical train stop arm as used on LUL among many metro systems is really just a more refined non-destructive version of that which can automatically engage brakes by means of a 'trip cock' valve.
I think that's part of the reason, but it's also to get the most safety-critical lamp closest to the driver's line of sight. For example on the rare occasions a colour light is mounted very low down (often as a "co-actor" to repeat a nearby high signal with poor sighting) the red is at the top. Of course in that case if it was at the bottom it might be obscured by debris on the ground...
Ground-mounted main signals, which are rare in the UK but not unknown, always have the red at the top to be closest to the driver's line of sight. Some tunnel signals are fairly low down to physically fit within the particular curved profile of the bore, and thus also have unusual aspect order arrangements.
 
Status
Not open for further replies.

Top